This invention relates to a device to automatically shut off an internal combustion engine upon exceeding operating limits of the engine. In particular, it relates to a device for shutting off a diesel engine by terminating fuel supply to the engine when oil pressure is below operating limits, or when either coolant temperature or oil temperature exceed operating limits. Provision is also included for engine shutoff by terminating fuel and air supply upon an overspeed condition.
Internal combustion engines, particularly diesel engines are dependent upon proper lubrication and proper cooling in order to operate. Such engines are usually manufactured with an engine oil pump and an engine oil sump. Lubricating oil is communicated from the engine sump to the engine oil pump wherein the lubricating fluid is pressurized to be communicated to various passages in the engine. The lubricant serves two purposes which are clearly interrelated. First the lubricant reduces friction between moving parts which by and of itself reduces engine temperature. The second purpose of the lubricant is to augment the cooling features of an engine. Since, in an internal combustion engine, heat is an inherent part of the engine, it is important to take advantage of every possible means for cooling the engine. Oil communicated to the various passages from the engine pump is returned to the sump either directly or in some cases in large engines through an engine oil cooler. In any event, the important factors of an engine lubrication system which are symptomatic of engine condition are engine oil pressure and engine oil temperature. A loss of engine oil pressure is a positive indication of potential engine failure. An increase in engine oil temperature, although not necessarily as critical a measure as a decrease of engine oil pressure, generally indicates a malfunction of some sort internally in the engine. In some cases an increase in engine oil temperature is an early indication of an engine oil leak.
Internal combustion engines of the type used in heavy construction equipment and the like generally are configured with a liquid coolant system. Such systems generally include a pump and a radiator, with the pump being driven by the prime mover. Liquid coolant is circulated through a jacket surrounding and usually integrally formed with the internal combustion engine wherein heat is picked up by the liquid coolant and is then circulated through a heat exchanger in the form of a radiator exterior of the engine. A fan is usually driven by the prime mover to circulate air through the radiator thus cooling the fluid for susbequent recirculation through the engine. Two common points of failure in a liquid coolant system are breakage of the coolant pump internal of the engine or loss of the fan drive to prevent cooling air being circulated through the radiator. In either event, or in the event of a puncture of the jacket or radiator with the consequent loss of cooling fluid, temperature of the remaining fluid rapidly increases with the concomitant rise in temperature of the engine itself. As previously indicated, an increase in temperature of the engine beyond a certain point results in early failure of the engine.
A third problem with internal combustion engines is associated with an overspeed condition. An overspeed can occur in an internal combustion engine, for example, as a result of the loss of the load on the engine. In a governed diesel engine the engine governor will usually protect the engine from overspeeding due to the loss of the load. Overspeeds occur in governed diesel engines because of a malfunctioning fuel system injecting excess fuel. A very likely possibility during an overspeed resulting from a fuel system malfunction is such rapid increase in engine speed that the operator is unable to shut down the engine before damage occurs. A loss of the load and a fuel system malfunction occurring simultaneously is especially serious. In the case of an engine driven heavy construction vehicle, this potential overspeed condition can occur during a long downhill run wherein the load is removed from the engine and the vehicle is free running. A similar overspeed condition can occur upon failure of the drive train of a heavy construction vehicle. In internal combustion engines utilized in a stationary environment, for example an engine driving a compressor or the like, a similar loss of load can occur on a failure of the drive train. Other events causing overspeed are well-known in the art. An overspeed condition can result in a catastrophic disassociation of the engine itself. Such failure is extremely hazardous to personnel working in the immediate vicinity in the engine, particularly a driver in a heavy construction vehicle who can be severely injured by such a failure.
Although it is possible for an operator to monitor the various gauges indicating engine oil pressure, engine oil temperature, coolant temperature and engine speed it is impractical to rely on continuous monitoring of the gauges during normal use of internal combustion engines. Furthermore, to rely on engine gauges themselves and consequent manual shutdown of an engine by an operator on knowledge of high oil pressure, high oil temperature, and the like has not proved reliable in every case. An over-zealous operator can be tempted to continue to operate his internal combustion engine notwithstanding a low oil pressure indication or a high engine coolant temperature indication or an overspeed indication. This, of course, assumes the operator has noted the condition. An overspeed indication is particularly insidious as momentary losses of loads can result in an overspeed condition. Although a single overspeed condition may not result in an immediate engine failure it is probable that a series of engine overspeeds could adversely affect the fatigue life of the various moving parts in the engine. Thus, it is appropriate to provide some means of stopping the engine upon an overspeed condition to reconnect the load or if necessary to allow for possible inspection of the moving parts before the engine is restarted. It is also appropriate to provide for stoppage of the engine upon sensing of low oil pressure or high engine coolant temperature for the same reason.
A particular problem, however, is associated with low oil pressure. An internal combustion engine is designed to operate at a normal or optimum speed wherein the engine oil pressure should remain above a minimum level. However, during certain periods between normal high r.p.m. periods of operation it is convenient to allow the engine to continue to run at a low r.p.m. or at an "idle" setting. Since the engine oil pump is generally driven directly by the engine, engine oil pressure becomes, in part, a factor of engine r.p.m. Therefore, at the low r.p.m. or "idle" setting, engine oil pressure usually will be below the minimum engine oil pressure for normal or optimum r.p.m. speeds. The engine, nevertheless, needs lubrication at the "idle" setting in the same manner it needs lubrication at the normal setting. Therefore it is appropriate to have a dual level engine oil pressure cutoff capability. This not only provides for a better system, it can preclude necessary override features of earlier engine cutoff systems. Such override systems were required because it was necessary to establish a certain level of oil pressure before the automatic cutoff feature could be utilized.